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On 1/27/2026 4:30 PM, Luck, Tony wrote: > On Wed, Jan 21, 2026 at 03:12:51PM -0600, Babu Moger wrote: >> @@ -138,6 +143,20 @@ static inline void __resctrl_sched_in(struct task_struct *tsk) >> state->cur_rmid = rmid; >> wrmsr(MSR_IA32_PQR_ASSOC, rmid, closid); >> } >> + >> + if (static_branch_likely(&rdt_plza_enable_key)) { >> + tmp = READ_ONCE(tsk->plza); >> + if (tmp) >> + plza = tmp; >> + >> + if (plza != state->cur_plza) { >> + state->cur_plza = plza; >> + wrmsr(MSR_IA32_PQR_PLZA_ASSOC, >> + RMID_EN | state->plza_rmid, >> + (plza ? PLZA_EN : 0) | CLOSID_EN | state->plza_closid); >> + } >> + } >> + > > Babu, > > This addition to the context switch code surprised me. After your talk > at LPC I had imagined that PLZA would be a single global setting so that > every syscall/page-fault/interrupt would run with a different CLOSID > (presumably one configured with more cache and memory bandwidth). > > But this patch series looks like things are more flexible with the > ability to set different values (of RMID as well as CLOSID) per group. Yes. this similar what we have with MSR_IA32_PQR_ASSOC. The association can be done either thru CPUs (just one MSR write) or task based association(more MSR write as task moves around). > > It looks like it is possible to have some resctrl group with very > limited resources just bump up a bit when in ring0, while other > groups may get some different amount. > > The additions for plza to the Documentation aren't helping me > understand how users will apply this. > > Do you have some more examples? Group creation is similar to what we have currently. 1. create a regular group and setup the limits. # mkdir /sys/fs/resctrl/group 2. Assign tasks or CPUs. # echo 1234 > /sys/fs/resctrl/group/tasks This is a regular group. 3. Now you figured that you need to change things in CPL0 for this task. 4. Now create a PLZA group now and tweek the limits, # mkdir /sys/fs/resctrl/group1 # echo 1 > /sys/fs/resctrl/group1/plza # echo "MB:0=100" > /sys/fs/resctrl/group1/schemata 5. Assign the same task to the plza group. # echo 1234 > /sys/fs/resctrl/group1/tasks Now the task 1234 will be using the limits from group1 when running in CPL0. I will add few more details in my next revision. Thanks Babu